Method of making feedthroughs for electrical connectors

ABSTRACT

A method ( 10 ) of forming an electrically conducting feedthrough. The method ( 10 ) comprises a first step ( 11 ) of forming an electrically conductive structure ( 21 ) comprising a sacrificial component and a non-sacrificial component. At least a portion of the non-sacrificial component can then be coated with a relatively electrically insulating material ( 35 ) prior to removal of at least a portion of the sacrificial component from the electrically conductive structure. The structure of the feedthrough provides electrical connection through the wall of a housing of an implantable component while preventing unwanted transfer of materials between the interior of the component and the surrounding environment.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.10/529,063, entitled “Feedthrough For Electrical Connectors,” filed onNov. 8, 2005 which claims the priority of and is a national stageapplication of PCT Application No. PCT/AU2003/001288, entitled,“Feedthrough for Electrical Connectors,” filed on Sep. 30, 2003, whichclaims the priority of Australian Patent No. 2002951734, AustralianPatent No. 2002951738, Australian Patent No. 2002951739, and AustralianPatent No. 2002951740 that were each filed on Sep. 30, 2002. The entiredisclosure and contents of the above applications are herebyincorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a method of forming relatively small orminiature electrical connector systems. More specifically, the presentinvention relates to a method of forming hermetically sealed butelectrically conducting feedthroughs for devices, including biosensorsand implantable devices. Electrically conducting feedthroughs are alsodescribed. Examples of implantable devices that can use suchfeedthroughs include the implantable component of a cochlear implanthearing prosthesis.

BACKGROUND OF THE INVENTION

The term ‘feedthrough’ as used herein refers to the provision of anelectrically conducting path extending through an insulative member,from one side of the insulative member to another. The electricallyconducting path may extend from the interior of a hermetically sealedcontainer or housing on one side of the insulative member, to anexternal location outside the container or housing on the other side ofthe insulative member. Typically, a conductive path is provided by anelectrically conductive pin, which is electrically insulated from thecontainer or housing by an electrically insulating body surrounding thepin.

A feedthrough device can therefore allow one or more electricalconnections to be made with electronic circuitry or components within anhermetically sealed container or housing, whilst protecting thecircuitry or components from any damage or malfunction that may resultfrom exposure to the surrounding environment.

There are many applications for feedthrough devices that provide anelectrically conducting path through the wall of a housing or containerwhilst also sealing the electrical container or housing from its ambientenvironment. Historically, the first such devices were widely used invacuum technology allowing for the transfer of signals between chambersof differing pressures. In such applications, the vacuum tubes had to besealed because they could only operate under low-pressure conditions.

Over time, and with the advent of electrical devices capable of beingimplanted in body tissue to provide therapy to a patient, such ascardiac pacemakers, defibrillators and cochlear implants, the need toprovide feedthrough devices with improved hermeticity has becomeincreasingly important. As the environment of living tissue and bodyfluids is relatively corrosive and devices may contain materials whichmay be detrimental if exposed to the patient, a hermetic feedthroughdevice is used to provide a barrier between the electronic components ofthe device and the external corrosive environment of the human body.With implantable medical devices in particular, it is criticallyimportant that the hermetic seal of the device be physically rugged andlong lasting. For this reason, stringent requirements are imposed on thehermeticity of an implanted device, typically requiring a seal thatprovides a leakage rate of less than 10⁻⁸ cc/sec.

Given this, feedthroughs used in medical implant applications, such asthose used in pacemaker devices and cochlear implants, typically consistof a ceramic or glass bead that is bonded chemically at its perimeterthrough brazing or the use of oxides, and/or mechanically bonded throughcompression, to the walls of the sealed package. A suitable wire orother conductor passes through the centre of the bead, and this wire orconductor must also be sealed to the bead through chemical bonds and/ormechanical compression. Such feedthroughs are typically cylindrical andthe wire(s) or conductor(s) mounted within the bead are centred ormounted in a uniform pattern, centrally within the bead.

Other materials and processes are known for making feedthroughs whichrely, for example, on use of aluminium oxide ceramic and binders. Thesetypes of feedthroughs are widely used for cardiac implants and cochlearimplants. One of the processes for making such a feedthrough consists ofpre-drilling holes in a sintered ceramic plate and then forcingelectrical conductive pins through the holes. While useful, this methodis tedious and slow and does not necessarily guarantee a hermetic sealand generally results in unsatisfactory leakage rates on testing and lowyields. A second method involves inserting the conductive pins into anunsintered (or ‘green’) ceramic plate and then curing the assembly byfiring to achieve a hermetic seal. A major disadvantage of this lastmethod is that, historically the manufacturing process has beenperformed by hand. Such a method of manufacture can lead to inaccuraciesand be time consuming, expensive and labour intensive. Moreover, thefeedthrough devices resulting from such a process do not necessarilyhave precisely positioned electrical conductors, with the position ofthe conductors being greatly dependent upon the process itself. Further,as the conductors are typically wires being of a general cylindricalshape and configuration, the size and shape of the conductor extendingfrom the insulative material of the feedthrough is generally the same asthe conductor embedded in the insulative material of the feedthrough.

As implantable devices continue to develop and become thinner, smallerand more electronically sophisticated, the requirements of thefeedthrough have also increased. In cochlear implants, for example,where there is presently typically somewhere between 22-24 electrodeleads, there is a need for 22-24 conductive pins passing through thefeedthrough device. As the desire for more electrodes and smallerfeedthroughs increases, the demands placed upon the design of thetraditional feedthrough also increases. The problems in fabricating sucha feedthrough device on such a large scale are therefore quitesignificant, especially when one considers the relatively high degree oflabour intensity and specialisation of current fabricating methods.

While the above described prior art feedthrough devices and fabricationmethods have proven successful, it is a relatively slow and labourintensive process to manufacture such devices. The method of manufactureof the feedthrough also presents limitations as to the construction ofthe feedthrough.

Any discussion of documents, acts, materials, devices, articles or thelike which has been included in the present specification is solely forthe purpose of providing a context for the present invention. It is notto be taken as an admission that any or all of these matters form partof the prior art base or were common general knowledge in the fieldrelevant to the present invention as it existed before the priority dateof each claim of this application.

SUMMARY OF THE INVENTION

Throughout this specification the word “comprise”, or variations such as“comprises” or “comprising”, will be understood to imply the inclusionof a stated element, integer or step, or group of elements, integers orsteps, but not the exclusion of any other element, integer or step, orgroup of elements, integers or steps.

The present invention is directed to a method of forming a feedthroughthat preferably addresses at least some of the problems with prior artprocesses.

The present invention also potentially allows more flexibility in thedesign of feedthrough devices by providing control over the position andconfiguration of the conductors through the device, the physical shapeand size of the device, the number of conductors used and the overallhermeticity of the feedthrough device.

According to a first aspect, the present invention is a method offorming an electrically conducting feedthrough comprising the steps of:

(i) forming an electrically conductive structure comprising asacrificial component and non-sacrificial component;

(ii) coating at least a portion of the non-sacrificial component with arelatively electrically insulating material; and

(iii) removing at least a portion of the sacrificial component from theelectrically conductive structure.

The electrically insulating material is preferably a ceramic material ora hermetic glass material suitable for use in a feedthrough application.

In one embodiment, the electrically insulating material can be coated onthe non-sacrificial component and not coated or moulded on to anyportion of the sacrificial component of the conductive structure. Inanother embodiment, the electrically insulating material can be coatedon the non-sacrificial component and at least a portion of thesacrificial component of the conductive structure. Still further, step(iii) can comprise removing at least that portion of the sacrificialcomponent on to which the insulative material has not been coated.

In one embodiment, the electrically conductive structure can be formedfrom an electrically conductive material. The electrically conductivematerial can be a metal, a metal alloy, an electrically conductiveceramic, an electrically conductive composite, or an intrinsically orextrinsically electrically conductive polymer. In a preferredembodiment, the structure is formed from a film or shim of electricallyconductive material. In one such embodiment, the electrically conductivestructure can be formed from a film or shim of platinum. Use of othermaterials such as iridium can be envisaged.

The film or shim can be formed into a shape comprising the sacrificialcomponent and the non-sacrificial component of the electricallyconductive structure. In this embodiment, it will be appreciated thatthat portion of the film or shim comprising the non-sacrificialcomponent may comprise more than one portion of the film or shim.Similarly, that portion of the film or shim comprising the sacrificialcomponent may comprise more than one portion of the film or shim.

In one embodiment, the electrically conductive component may comprise afilm or shim having a shape comprising two or more separated conductiveelements extending between respective transverse support members. Theseconductive elements can be substantially elongate. In a furtherembodiment, the film or shim can have at least ten separatedsubstantially elongate members extending between the respective supportmembers. In one embodiment, the support members are substantiallyparallel with respect to each other. Still further, the support memberscan be straight and in a parallel arrangement. In another embodiment, atleast one, and preferably all, of the conductive elements can benon-linear. In another embodiment, at least one, and preferably all, ofthe conductive elements can have a length that is greater than theshortest distance between the respective transverse support members. Ina still further embodiment, the surface of at least one, and preferablyall, of the conductive elements can be non-linear and/or define aninterface path between the conductive element and the insulatingmaterial that is longer than the shortest distance between therespective transverse support members.

The separation of the conductive elements is preferably such that theelectrically insulating material can be coated between the elements andso prevent electrical conduction between the respective elements atcompletion of the method according to the first aspect.

In a preferred embodiment, the shape of the electrically conductivecomponent can be formed in step (i) by punching the shape, using asuitably shaped and dimensioned punching tool, from a film ofelectrically conductive material, such as platinum.

In another embodiment, the shape of the electrically conductivecomponent can be formed in step (i) by using electrical dischargemachining (EDM), which is also known as spark erosion, to removeunwanted portions of the film. In a preferred embodiment, the EDMequipment used in the process has a cutting tool comprising anelectrode. The cutting tool does not physically cut the sheet butinstead relies on the equipment generating a series of electricaldischarges between the electrode and the film in a dielectric fluid. Theelectrical discharges serve to vaporise the film in the region adjacentthe cutting tool.

In a preferred embodiment, the cutting tool has a size and shape thatmatches the size and shape of the portion of the film to be removed fromthe film during the machining steps. In this embodiment, it is preferredthat the tool is brought adjacent the film at a number of differentlocations so as to remove differing portions of the film. This multipleuse of the tool preferably serves to gradually build up the pattern ofthe electrically conductive component.

In a preferred embodiment, the cutting tool can be used to form a seriesof discrete linear conductive members from a film of platinum or othersuitable metal or metal alloy. The linear conductive members can bealigned in a parallel arrangement.

In another embodiment, the cutting tool can be used to form a series ofdiscrete linear conductive members from a plurality of films of platinumor other suitable material stacked one atop the other. In this manner, alarge number of electrically conductive components can be prepared witha single cutting motion of the cutting tool. In such an embodiment, amethod known as “wire cutting” can be employed. This method operates ina similar manner to EDM/spark erosion methods wherein a wire is passedthrough a stack of films or foils of conductive material with this wirebecoming the electrode causing the erosion of material adjacent theelectrode. By using this method a plurality of films or foils can bepatterned simultaneously, resulting in a process that is capable of massproducing patterned conductive films or foils to be used to create thefeedthrough device of the present invention.

In the method, at least a portion of each of the substantially elongatemembers extending between the support members are coated with theelectrically insulating material (step (ii) is described in more detailbelow). As mentioned, the electrically insulating material can bealumina but other suitable ceramic types can be envisaged.

In another embodiment, the step of forming the electrically conductivestructure can comprise the steps of:

(a) forming a relatively electrically insulating disc having an outerperiphery defining a plurality of outwardly extending teeth havingnotches therebetween; and

(b) winding an electrically conductive element around the disc such thatat least some of the notches have a portion of the conductive elementpassing therethrough.

In this embodiment, the electrically insulating disc can be formed of aceramic material such as alumina. The disc can have a plurality ofequally spaced notches and teeth about its outer periphery.

In this embodiment, each of the notches can receive a conductiveelement. Preferably, a single metal wire is used for each disc. The wirepreferably comprises platinum wire. The wire can have a diameter ofabout 25 μm.

Once the conductive element has been wound about the disc and passedthrough each of the notches, the insulating disc and surroundingconductive element can be overmoulded with a coating of insulatingmaterial as defined in step (ii) of the method described above. Thoseportions of the conductive element not extending through the feedthroughcan then be removed.

In a still further embodiment, the step of forming the electricallyconductive structure comprises a step of forming a sheet of platinumhaving a plurality of integrally attached substantially elongate membersextending outwardly from at least a portion of the periphery thereof. Ina preferred embodiment, the elongate members extend outwardly and in adirection out of the plane of the sheet. For example, the elongatemembers can extend outwardly and upwardly from the sheet. In thisembodiment, the elongate members can be rectangular in shape.

In this embodiment, the sheet can be rectangular or square. In thisembodiment, at least three sides of the sheet can have elongate membersextending at least out of the plane of the sheet.

In a still further embodiment, the step of forming the electricallyconductive structure comprises a step of spirally coiling anelectrically conductive wire, such as platinum wire, along at least aportion of a length of a screw thread. Once positioned, an insulatinglayer can be moulded around the thread and the wire. Once the insulatinglayer has cured, the screw thread can be withdrawn from the insulatingmaterial so leaving the coiled wire embedded within the inner surface ofthe insulating layer.

The step of coating the electrically conductive structure preferablycomprises a step of mounting or clamping the conductive structure in amould and then moulding a coating of the insulating material on and/oraround the conductive structure.

Where the conductive structure comprises a plurality of substantiallyelongate members formed from a film or shim of, for example, platinum,the insulating material is preferably coated or moulded around at leasta portion of the substantially elongate members of the conductivestructure. In this embodiment, said portion of the substantiallyelongate members comprises a portion of the non-sacrificial component ofthe electrically conductive structure. While this embodiment envisagesthe film or shim being shaped as desired prior to clamping or mountingin the mould, it will be appreciated that a film could be firstlymounted or clamped in the mould and then shaped or punched as requiredprior to the moulding or coating step.

Where the conductive structure comprises an insulative disc having anotched outer surface and a conductive element passing through thenotches around the disc, the insulating material is preferably mouldedaround the disc such that at least those portions of the conductiveelement passing through the notches of the disc outer surface areencapsulated in the insulating material.

Where the conductive structure comprises a sheet having a plurality ofsubstantially elongate members extending at least out of the plane ofthe sheet, the insulating material is preferably moulded to both sidesof the sheet and elongate members, thereby encapsulating at least aportion of the members in the insulating material.

Where the conductive structure comprises a coiled wire embedded withinthe inner surface of an insulating layer, the orifice left by thewithdrawal of the screw thread can be filled with insulating material.

In a preferred embodiment, the mould can comprise an injection mould. Inone embodiment, step (ii) of the method can comprise a step of usingpowder injection moulding (PIM) to mould the insulating material aroundthe desired portion of the conductive structure.

In this moulding process, insulating material such as fine ceramicpowder is mixed with a carrier chemical, typically called binder, andhomogenised to create a feedstock for the injection mould. The presenceof the binder serves to make the feedstock sufficiently fluid to be usedin an injection moulding process. Once moulded, the insulating materialcan be allowed to at least partially set. The resulting moulded part ishereinafter called the green body.

Once the green body is formed, the sacrificial component of theelectrically conductive structure can be removed. During this step, itis possible that a portion of the green body may also need to beremoved. In one embodiment, the sacrificial component can be removed bybeing cut, abraded or ground away. In this regard, physical cutting witha knife, or laser cutting techniques, are envisaged.

Where the electrically conductive structure comprises the plurality ofsubstantially elongate members extending between the transverse members,the sacrificial component preferably includes at least the transversesupport members so leaving a plurality of electrically insulatedelongate members extending through the green body.

Where the electrically conductive structure comprises an insulating dischaving a conductive element, such as a wire, passing through a pluralityof notches, the sacrificial component can comprise at least some of thatpart of the conductive element not passing through the notches. Onremoval of the remainder of the conductive element, one is left with aninsulative member having a conductive member passing therethrough ateach location where a notch existed in the outer surface of the originalinsulative disc.

Where the electrically conductive structure comprises a sheet having aplurality of substantially elongate members extending at least out ofthe plane of the sheet, the sacrificial component preferably comprisesthe sheet from which each of the elongate members extend. With the sheetand substantially elongate members supported on one side by aninsulative layer, the sheet can be punched from the structure leaving aring of insulating material with the now separated elongate conductivemembers supported thereon. Another layer of insulating material can thenbe moulded between and around the ring thereby forming an insulatingmember having the elongate members extending therethrough from one faceto the other.

Where the electrically conductive structure comprises a coiled wireembedded within an insulating coating, the sacrificial componentpreferably comprises adjacent portions of respective turns of the coiledwire.

In a still further embodiment, the method can comprise an additionalstep of debinding the green body. In this step, any binder in the greenbody is preferably extracted from the insulative material. In oneembodiment, this step can comprise a chemical debinding in which thegreen body is soaked in a suitable solvent. In another embodiment, thisstep can comprise exposing the green body to a relatively elevatedtemperature. This temperature is preferably sufficient to boil off thebinder from the green body while not causing the green body to undergosintering. In one embodiment, the temperature is between about 150° C.and 200° C.

During the debinding step, the insulating material preferably shrinks indimension. This debinded insulating material member is hereinaftercalled a brown body.

When ready, the brown body can undergo a sintering step. The sinteringstep preferably comprises exposing the brown body to a suitable elevatedtemperature. In one embodiment, the sintering step can comprise exposingthe brown body to a sintering temperature of about 1700° C. During thesintering step, the insulating member undergoes further shrinkage andbecomes relatively more robust. The shrinkage of the insulating memberalso serves to form a hermetic seal at the interface between theembedded conductive members and the surrounding sintered insulatingmember.

Once complete, the insulating member with the conductive membersextending therethrough can be brazed into an orifice in the wall of aunit adapted to receive the feedthrough. Electrical connection can thenbe made to each end of the respective conductive members as required toform respective electrical conductive paths through the insulating bodyof the feedthrough.

According to a further aspect, the present invention is a feedthroughformed using one of the methods described herein.

According to a still further aspect, the present invention is afeedthrough comprised of one or more relatively electrically conductivestructures extending through and embedded within a relativelyelectrically insulating body, wherein the one or more electricallyconductive structures are formed from a film or shim of an electricallyconductive metal or metal alloy.

In one embodiment, the electrically conductive structures have anoverall elongate length of at least 7 mm and, more preferably, about 7.8mm. In a further embodiment, the width of the conductive structures ispreferably between about 1.5-2.5 mm. In a still further embodiment, thefilm or shim from which the conductive structures are formed preferablyhas a thickness of between about 40 and 70 microns, more preferablyabout 50 microns.

In one embodiment of this aspect, the electrically conductive structurescan be formed using one of the methods according to the first aspect ofthe invention.

According to yet another aspect, the present invention is anelectrically conducting feedthrough comprising:

a relatively electrically insulating member having a first face and atleast a second face; and

at least one electrically conductive member extending through at least aportion of the electrically insulative member from the first face to thesecond face;

wherein said at least one conductive member is non-linear between saidfirst face and said second face.

According to yet a further aspect, the present invention is anelectrically conducting feedthrough comprising:

a relatively electrically insulative member having a first face and atleast a second face; and

at least one relatively electrically conductive member extending throughat least a portion of the electrically insulative member from the firstface to the second face;

wherein said at least one conductive member has a length between saidfirst face and second face that is greater than the shortest distancebetween said first face and said second face.

According to a still further aspect, the present invention is anelectrically conducting feedthrough comprising:

a relatively electrically insulative member having a first face and atleast a second face; and

at least one relatively electrically conductive member having an outersurface and extending through at least a portion of the electricallyinsulative member from the first face to the second face;

wherein at least a portion of the outer surface of said at least oneconductive member is non-linear between said first face and said secondface.

According to yet another aspect, the present invention is anelectrically conducting feedthrough comprising:

a relatively electrically insulative member having a first face and atleast a second face; and

at least one relatively electrically conductive member having an outersurface and extending through at least a portion of the electricallyinsulative member from the first face to the second face;

wherein at least a portion of the outer surface of said at least oneconductive member defines an interface path between the conductiveelement and the insulating material that is greater than the shortestdistance between said first face and said second face.

In one embodiment, the first face and second face of the insulatingmember can face outwardly in opposite directions. In one embodiment, thefirst and second faces can be substantially parallel or parallel. Thefirst face is preferably the outer face of the feedthrough and thesecond face is preferably the inner face of the feedthrough.

In one embodiment, the feedthrough preferably has a plurality ofelectrically conductive members extending through the insulative memberfrom said first face to said second face. In one embodiment, each of theconductive members has the same configuration. In another embodiment,only some of the conductive members may have the same configurationwhile one or others have a different configuration.

In a further embodiment, said one or more conductive members can undergoa first change of direction between the first face and the second faceof the insulative member. In another embodiment, said one or moreconductive members can undergo two or more changes of direction betweenthe first face and the second face of the insulative member.

In yet another embodiment, said one or more conductive members undergo achange of direction in a nominal plane extending at an angle, such as aright angle, to one or both faces of the insulative member. In anotherembodiment, said one or more conductive members can undergo a change ofdirection into a direction out of a nominal plane extending at an angle,such as a right angle, to one or both faces of the insulative member.The conductive member can undergo more than one change of direction outof said nominal plane.

Each change of direction can be at a right angle to the precedingdirection of the conductive member. In another embodiment, the change ofdirection can be at a different angle than a right angle to that of thepreceding direction.

In another embodiment, the change of direction can be abrupt. In anotherembodiment, the change of direction can be smoothly curved. In anotherembodiment, a particular conductive member can undergo a combination ofabrupt and/or smoothly curved changes of direction.

In yet another embodiment, said one or more conductive members can havea shape of varying cross-section over the length thereof. In thisregard, the conductive members may extend linearly or non-linearlythrough the insulative member, however, the interface path between theconductive members and the insulative member is maximised, therebyreducing the effective leakage pathway of the feedthrough device. Theconductive members may have a stepped shape providing a zig-zaginterface pathway or may have a screw-thread shape providing an equallyextended interface pathway.

According to another aspect, the present invention is an electricallyconducting feedthrough comprising:

a relatively electrically insulating member having a first face and atleast a second face; and

a plurality of electrically conductive members each having a first endand a second end and extending through at least a portion of theinsulative member from said first end at or adjacent the first face tosaid second end at or adjacent the second face of the insulative member;

wherein the configuration of the first ends of the conductive members ator adjacent the first face of the insulative member is different to theconfiguration of the second ends of the conductive members at oradjacent the second face of the insulative member.

In this aspect, the respective configurations of the first ends and thesecond ends of the conductive members can be such that the number offirst ends of the conductive members per a defined unit area at oradjacent the first face of the insulative member is different to thenumber of second ends of the conductive members per said defined unitarea at or adjacent the second face of the insulative member.

In one embodiment, the number of first ends per defined unit area can begreater than the number of second ends per said defined unit area. Inanother embodiment, the number of first ends per defined unit area canbe less than the number of second ends per said defined unit area.

In this embodiment, the defined unit area can be 1 mm², 1 cm², or someother area.

Still further, the respective configurations of the first ends and thesecond ends of the conductive members can be such that the spacingbetween the first ends of the conductive members at or adjacent thefirst face of the insulative member is different to the spacing betweenthe second ends of the conductive members at or adjacent the second faceof the insulative member.

In this embodiment, the spacing between the first ends of the conductivemembers can be greater than the spacing between the second ends of theconductive members. In another embodiment, the spacing between the firstends of the conductive members can be less than the spacing between thesecond ends of the conductive members.

In each of these aspects, the feedthrough can comprise two or moregroups of said plurality of electrically conductive members. Eachconductive member in a group can be identical in configuration to theother conductive members in a group. In another embodiment, at least oneconductive member in a group can be different in configuration to one orall of the other conductive members in that group. In anotherembodiment, the conductive members of one group can be different inconfiguration to one or more of the conductive members of another groupof the feedthrough. Still further, the conductive members of one groupcan be identical in configuration to one or more of the conductivemembers of another group of the feedthrough.

In one embodiment, each feedthrough comprises two, three or more groupsof conductive members. Each group can comprise a series of conductivemembers in side-by-side relationship. This embodiment offers thecapability of the feedthrough having a plurality of layers of conductivemembers. Such layers of conductive members can be off-set from adjacentlayers.

In yet another embodiment, the respective dimensions and shape of thefirst ends and second ends of the conductive members can be such thattheir shape and dimensions can differ between the first ends at oradjacent the first face of the insulative member and the second ends ator adjacent the second face of the insulative member. Equally, the shapeand dimensions of the first and second ends of the conductive memberscan also differ from the shape and dimensions of the conductive memberembedded within the insulative member.

In this embodiment, the shape and dimensions of the first ends of theconductive members can be such as to allow the ends to communicatedirectly with an integrated chip design whilst the shape and dimensionsof the second ends of the conductive members can be such as to allow theends to communicate with wires or leads connected to a stimulatingelectrode or the like. In this regard, the size and shape of the firstand second ends of the conductive members can be determined prior to themanufacture of the feedthrough device.

In these aspects, the relatively electrically insulative material ispreferably a ceramic material or hermetic glass material, suitable foruse in a feedthrough application.

Still further, the hermeticity of the interface between each of theinterfaces between the respective electrically conductive structures andthe relative insulative body or the degree of permeation of fluidbetween the conductive structure and the insulative body is preferablydefined by the following relationship:H=f(L,1/A,1/t)  (1)where

-   -   L is the length of the electrically conductive element extending        from a first face to a second face of the insulative body;    -   A is the cross-sectional area of the electrically conductive        element; and    -   t is the time that the interface is exposed to the fluid,        including bodily fluids.

It will be appreciated that the cross-sectional area A is related to ameasurement of the perimeter of the electrically conductive element.That is, the smaller the size of the interface between the conductiveinsert and the insulative material, the greater the degree ofhermeticity of the feedthrough.

In one embodiment, the feedthrough can be brazed into the wall of anelectrical device, such as an implantable stimulator unit of a medicalimplant device. In a preferred embodiment, the feedthrough can beadapted to be used with a cochlear implant hearing prosthesis to provideelectrical conduction between the circuitry within an implantablestimulator unit and the intracochlear or extracochlear electrodes and/orthe implantable receiver coil.

Each feedthrough preferably has sufficient conductive members embeddedtherein to ensure there are sufficient connectors to suit the desiredapplication. In a cochlear implant application, the feedthrough wouldpreferably have sufficient conductive members embedded therein to ensurethat there are sufficient connectors for each of the electrode channelsof the intracochlear electrode array, one or more extracochlearelectrodes, and the inputs from the receiver coil.

The present invention provides a method of forming a feedthrough for animplantable component comprising a relatively electrically insulativemember having a plurality of relatively electrically conductive membersextending therethrough. The method ensures the electrically conductivemembers are hermetically encased within the insulating material in a waythat allows electrical connection through the feedthrough whilepreventing transfer of bodily fluids from outside the component into theinterior of the component, as well as preventing the transfer ofpotentially dangerous materials from internal of the component to thesurrounding tissue and body fluids.

The present invention also provides the capability of using smallersized conductive components, having a smaller perimeter of the crosssection, thereby providing increased hermeticity. It is thereforepossible to utilise the present invention to create feedthrough devicesthat are of similar dimensions to prior art feedthrough devices butwhich have far superior hermeticity properties. Equally, the presentinvention can be utilised to create feedthrough devices which are ofmuch smaller dimensions than existing feedthrough devices having similarand improved hermeticity than is currently the case.

The present invention also provides the ability to create a feedthroughdevice having a relatively denser array of conductive structures thanprior art devices, as the conductive components can be spaced closertogether than is achievable in traditional devices.

According to a further aspect, the present invention is a method offorming an insulative member of a feedthrough device comprising the stepof moulding the member in a mould having a plurality of pins extendingtherethrough.

In this embodiment, the mould can have a desired number of pins, forexample 28, in one plate of the mould and a corresponding number ofcavities, accommodating the pins, in the opposite plate of the mould. Inuse, the mould is filled with hot feedstock and in order to prevent thepressure of the injection from bending the pins and to minimize impactduring injection, the mould is only partially opened when the initialquantity of the feedstock is injected. As the mould cavity is onlypartially opened, only a very short portion of the pins are exposed tothe pressure. The mould is then slowly opened while injection continues,so that at any given time only a very short portion of the pins areexposed unsupported to the injection of the feedstock. Eventually, theentire cavity of the mould is filled while the position of the pins ispreserved. Once the moulding step is concluded, the moulded part can beejected from the mould, leaving behind the mould with its elongate pinsin place.

The moulded part ejected from the mould is left with a plurality ofholes therein formed by the presence of the pins in the mould. The holescan be about 175 μm in diameter.

The moulded part can then undergo further processing. For example,platinum pins can be inserted into the holes of the moulded part beforethe entire assembly undergoes a water de-binding step, which includeswashing of the moulded part over several hours at an elevatedtemperature, e.g. 40° C. The assembly can then undergo thermalde-binding at approximately 300° C. over a period of approximately 24hours. Finally, the assembly can be sintered at around 1600° C. therebyforming a final assembly that has a series of platinum pins extendingtherethrough.

In another aspect, the present invention is a method of forming aninsulative member of a feedthrough device comprising the steps of:

forming a sacrificial component having a plurality of elongatestructures;

coating at least a portion of the elongate structures with a relativelyelectrically insulating material; and

sacrificing the sacrificial component so leaving an electricallyinsulating material having a plurality of holes therein at what was thelocation of the elongate structures.

In this aspect, the sacrificial component can have a shape similar to oridentical to that depicted in FIGS. 1, 14, 15, 16, 17 and 20. Othershapes, such as annular arrangements of elongate structures can beenvisaged. In this embodiment, however, the entire component is adaptedto be sacrificed so leaving a formed insulative member having aplurality of holes extending therethrough corresponding to the positionof the elongate members of the sacrificed component.

In one embodiment, the sacrificial component can comprise a metal orpolymer having a melting point less than that of the insulative memberformed therearound. Once the insulative member is formed, thetemperature of the member can be increased until such time as the metalor polymer of the sacrificial component melts and is drained or drawnaway from the insulative member. In this regard, it will be appreciatedthat the insulative member could be formed using an annular sacrificialcomponent that is melted away so leaving the member with its holesformed in the location of the now melted sacrificial component.

BRIEF DESCRIPTION OF THE DRAWINGS

By way of example only, preferred embodiments of the invention are nowdescribed with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of one embodiment of an electricallyconductive structure for use in the method according to the presentinvention;

FIG. 2 is a perspective view of the conductive structure of FIG. 1overmoulded with an insulative ceramic member;

FIG. 3 is a perspective view of the feedthrough formed from theconductive structure of FIG. 1;

FIG. 4 a is a perspective view of an insulative ceramic disc having asaw-tooth outer surface for use in the formation of another embodimentof a conductive structure according to the present invention;

FIG. 4 b is a perspective view of the ceramic disc of FIG. 4 a with aconductive platinum wire coiled around the disc;

FIG. 5 is a perspective view of the disc of FIG. 4 b with an overmouldof ceramic material around the outer surface of the disc;

FIG. 6 is a feedthrough formed from the conductive structure of FIG. 4a;

FIG. 7 is a perspective view of a platinum sheet with elongate membersextending out of the plane thereof for use as a conductive structure inanother embodiment of a method according to the present invention;

FIGS. 8 a and 8 b are perspective views of the sheet of FIG. 7 with alayer of ceramic moulded thereto;

FIG. 9 is a perspective view of a feedthrough formed using the sheet ofFIG. 7;

FIGS. 10 a-10 e are perspective views of a still further embodiment forforming a feedthrough using the method according to the presentinvention;

FIG. 11 is a simplified flow chart of the steps of one embodiment of themethod according to the present invention.

FIG. 12 a is a side view of a stack of platinum sheets about to bemachined into an electrically conducting feedthrough according to thepresent invention;

FIG. 12 b is a top view of a platinum sheet highlighting the region ofplatinum to be removed in the process depicted in FIG. 12 a;

FIG. 12 c is a top view of machined sheet of platinum formed using theprocess depicted in FIG. 12 a;

FIGS. 13 a-13 d depict another possible technique for forming afeedthrough according to the present invention;

FIG. 14 is a plan view of another embodiment of an electricallyconductive structure for use in the method according to the presentinvention;

FIG. 15 is an enlarged plan view of a single conductive member ofanother embodiment of a conductive structure according to the presentinvention;

FIG. 16 is an enlarged plan view of a single conductive member ofanother embodiment of a conductive structure according to the presentinvention;

FIG. 17 is an enlarged view of a single conductive member of anotherembodiment of a conductive structure according to the present invention;

FIG. 18 is a cross-sectional view of two different conductive structuresof a feedthrough according to the present invention wherein theinterface between the conductive structures and the insulative materialis non-linear;

FIG. 19 is an enlarged view of one of the interfaces of FIG. 18;

FIG. 20 is a plan view of yet another embodiment of an electricallyconductive structure for use in the manufacture of a feedthroughaccording to the present invention;

FIG. 21 is a plan view of the electrically conductive structure of FIG.20 embedded within a ceramic member with its transverse support membersremoved;

FIG. 22 is a sectional view of another embodiment of a feedthroughhaving three groups of conductive members;

FIG. 23 is a sectional view of another embodiment of a feedthroughaccording to the present invention;

FIG. 24 is a sectional view of a still further embodiment of afeedthrough according to the present invention;

FIG. 25 is a further part-sectional, part front view of the feedthroughof FIG. 24; and

FIG. 26 is a perspective of another embodiment of an insulative memberaccording to the present invention.

FIG. 27 is a perspective view of an implantable medical device to whicha feedthrough according to the present invention is electricallycoupled.

FIG. 28 a is a partial perspective view of an implantable medical deviceto which a feedthrough according to the present invention iselectrically coupled.

FIG. 28 b is a perspective view of an embodiment of a feedthroughaccording to the present invention.

FIG. 28 c is a partial perspective view of an implantable medical deviceafter a feedthrough according to the present invention has beenelectrically coupled.

PREFERRED MODE OF CARRYING OUT THE INVENTION

The steps of one embodiment of a method of forming an electricallyconducting feedthrough according to the present invention are depictedin FIG. 11.

The method 10 comprises a first step 11 of forming an electricallyconductive structure comprising a sacrificial component andnon-sacrificial component. Different examples of such structures aredepicted in FIGS. 1, 4 b, 7, and 10 b.

The method further comprises a step 12 of coating or moulding anon-electrically conductive insulative member on to at least a portionof the non-sacrificial component and not on to at least a portion of thesacrificial component of the conductive structure.

Still further, the method comprises a step 13 of then removing at leastthat portion of the sacrificial component of the conductive structure onto which the insulative member has not been coated or moulded.

Following removal of the sacrificial component of the conductivestructure, the green body of the insulator can undergo a step ofdebinding 14 prior to a step of sintering 15. Once sintered, the ceramicfeedthrough with the conductive members extending therethrough is readyfor appropriate mounting in the wall 278 of an implantable stimulatorunit 276 of a cochlear implant hearing prosthesis 270 or otherappropriate device.

The above sequence of steps are generally governed by the properties ofthe insulative member being employed, for example, ceramic shrinks whensintered. In this regard, it may be possible to vary the sequence of thesteps so that removal of at least a portion of the sacrificial componentoccurs after de-binding or sintering of the ceramic.

As depicted in FIG. 1, the electrically conductive structure formed instep 11 can be formed from a film or shim 21 of biocompatible platinum.Other suitable electrically conductive metals or metal alloys are alsoenvisaged.

As depicted in FIG. 1, the film or shim 21 of platinum can be formedinto a shape comprising the sacrificial component and thenon-sacrificial component of the electrically conductive structure. Inthis embodiment, the electrically conductive structure comprises aplurality of separated elongate linear members 22 extending betweenrespective parallel transverse support members 23,24.

The separation of the elongate members 22 is such that the insulativematerial when moulded around the members 22 can also move between themembers 22 and so prevent electrical conduction between the respectivemembers 22 at completion of the method 10.

In the depicted embodiment, the shape of the electrically conductivestructure 21 is formed by punching the shape, using a suitable shapedand dimensioned punching tool, from a film of platinum. It is envisagedthat this shape could be created by a variety of material removalmethods, such as electrical discharge machining (EDM), micro-knifingand/or laser cutting.

FIGS. 12 a, 12 b and 12 c depict one method of forming the electricallyconductive structure according to a preferred embodiment. In thismethod, wire cutting is utilised. This method employs the principles ofEDM methods to remove the unwanted material, however, in this instancethe spark is created between the work-piece 60 being machined, forexample a stack of platinum films 62, and a continuously moving wire 64,with the components immersed in a dielectric medium (not shown).

FIG. 12 a is a side view of this method and shows a number of foils ofconductive material 62 stacked together to form a work-piece 60, withthe foils preferably being clamped together and immersed into adielectric medium. The foils can be platinum or iridium or any othersuitable conductive material. The wire 64 is then fitted through thework-piece 60 by creating an appropriate aperture through the work-piece60. A series of electrical discharges are then generated between thewire 64 and the work-piece 60 in the dielectric medium, causing erosionof the films 62 to occur in a desired pattern. Typically, the wire 64 isdrawn through the work-piece 60 in a continuous feeding motion, forexample in a downward motion shown by arrow A, however, the position ofthe wire 64 with respect to the work-piece 60 can remain stationary,while the work-piece 60 is moved in the desired directions to createdthe desired pattern.

As is shown in FIG. 12 b, the hashed regions 66 are removed from each ofthe foils of conductive material in the work-piece 60. This then leavesa conductive film as depicted in FIG. 12 c as the cross-hashed region68, which is substantially the same as that shown and described withreference to FIG. 1.

It is also envisaged that the electrically conductive structures asdepicted in the drawings can be formed by metal injection moulding(MIM). Like PIM described above for forming the electrically insulativelayer, MIM uses metal powder instead of ceramic powder as in PIM, tocreate feedstock. In MIM, the structure is moulded and then undergoesde-binding and sintering to form the final structure. Such a method offorming the structure may be particularly useful in forming structureswith complex three-dimensional shapes, such as those described below.MIM may also be particularly useful in forming structures having variouscross-sectional shapes. In this regard, MIM techniques can formstructures having different profiles and smoother finishes than cancurrently be achieved with the above mentioned material removal methods.

As depicted in FIG. 2, at least a portion of each of the elongatemembers 22 extending between the support members 23,24 are coated orovermoulded with an insulative material 25 described in more detailbelow.

In the depicted embodiment, the step of moulding the insulative material25 around the electrically conductive structure (step 12) comprises astep of mounting or clamping the conductive structure in a mould andthen moulding the insulative material on and/or around the conductivestructure.

In a preferred embodiment, the mould can comprise an injection mould. Inone embodiment, step 12 can comprise a step of using powder injectionmoulding (PIM) to mould the insulative material around the desiredportion of the conductive structure. In a preferred embodiment of thismoulding process, fine ceramic powder is mixed with a binder andhomogenised to create a feedstock for the injection mould. The presenceof the binder serves to make the feedstock sufficiently fluid to be usedin an injection moulding process. Once moulded, the insulative ceramiccan be allowed to at least partially set and form a green body.

Once the green body is formed, the sacrificial component of theelectrically conductive structure can be removed. In the embodimentdepicted in FIGS. 1 to 3, the sacrificial component can be removed bylaser cutting. Other suitable material removal techniques, such ascutting or abrading techniques are also envisaged.

In the embodiment depicted in FIGS. 1 to 3, the sacrificial componentcomprises the transverse members 23,24. Once these are removed, aplurality of respectively electrically insulated elongate members 22remain extending through the green body 25.

In the embodiment depicted in FIGS. 4 a and 4 b, the step 11 of formingthe electrically conductive structure comprises the steps of:

(a) forming an insulative disc 30 having an outer surface defining aplurality of teeth 31 having notches 32 therebetween; and

(b) winding a platinum metal wire 33 around the disc 30 such that atleast some of the notches 32 have a wire passing therethrough (as isdepicted in FIG. 4 b).

In the depicted embodiment, the insulative disc can be formed of aceramic material such as that used in step 12 described above. Inanother embodiment, a different material could be used that exhibits thedesired insulative properties. The insulative disc 30 preferably has aplurality of equally spaced notches and teeth about its outer periphery.

As depicted in FIG. 4 b, each of the notches 32 receive a portion of thewire 33. In the depicted embodiment, the wire has a diameter of about 25μm.

Once the wire 33 has been passed through each of the notches 32, theinsulative disc 30 and surrounding wire can be overmoulded in step 12with an outer annular coating of a suitable insulative material such asa ceramic 35. This material is preferably moulded around the disc suchthat at least those portions of the wire 33 passing around the notches32 of the disc outer surface are encapsulated in the material 35.

The sacrificial component of the structure depicted in FIG. 5 comprisesthat part of the wire not passing through the notches 32. On removal ofthe remainder of the wire, one is left with an insulative member 35having a platinum conductive member 36 passing therethrough at eachlocation where a notch 32 existed in the outer surface of the originalinsulative disc 30.

Another method of forming a different conductive structure is depictedin FIGS. 7 to 9. In this arrangement, step 11 comprises forming amulti-sided sheet 40 of electrically conductive material, such asplatinum, having a plurality of integrally attached elongate members 41extending outwardly from at least three sides of the periphery thereof.The elongate members extend outwardly and in a direction out of theplane of the sheet. In the depicted arrangement, the elongate members 41extend outwardly and upwardly from the sheet.

In this embodiment, a coating of insulative material 42 is firstlymoulded to one side of the sheet 40 and elongate members 41.

In this embodiment, the sacrificial component preferably comprises thesheet 40 from which each of the elongate members 41 extend. With thesheet and elongate members supported on one side by a layer ofinsulative material 42, the sheet 40 can be removed from the structureleaving a ring of insulative material with the now separated elongatemembers 41 supported thereon. Another layer of insulative material 43can then be moulded between and around the ring thereby forming aninsulative member having the elongate members extending therethroughfrom one face to the other. The result is a plurality of respectivelyelectrically insulated elongate members 41 embedded within a ceramicgreen body comprised of layers 42 and 43.

In another embodiment depicted in FIGS. 10 a-10 e, the step of formingthe electrically conductive structure can comprise a step of spirallycoiling an electrically conductive wire 52, such as platinum wire, alongat least a portion of a length of a thread of a screw 51. Oncepositioned, a layer of insulative material 53 can be moulded around thethread 51 and the wire 52. Once the insulative material 53 has cured,the screw 51 can be withdrawn from the insulative ceramic material soleaving the coiled wire 52 embedded within the inner surface of theinsulator layer 53 (see FIG. 10 c). The orifice left by the withdrawalof the screw 51 can be filled with insulative material 54. In thisembodiment, the sacrificial component preferably comprises adjacentportions of respective turns of the coiled wire 52, so leaving wireportions 55 embedded within an insulative member as depicted in FIG. 10e.

FIGS. 13 a-13 b depict a still further embodiment of a method forforming a feedthrough according to the present invention. In thisembodiment, a series of platinum conductive members 71 are formed on acopper backing 72 (FIG. 13 a). A first layer of ceramic 73 can then bemoulded thereto (FIG. 13 b) before the copper backing is etched away(FIG. 13 c). An overmould of ceramic 74 is then provided (see FIG. 13 d)to form the completed feedthrough.

FIG. 14 depicts another type of electrically conductive structure thatcan be used in the manufacture of a feedthrough according to the presentinvention. The depicted electrically conductive structure is againformed from a film or shim 21 of biocompatible platinum.

In FIG. 14, the film or shim 21 of platinum is formed into a shapecomprising a sacrificial component and a non-sacrificial component. Inthis embodiment, the electrically conductive structure comprises aplurality of separated non-linear members 22 a extending betweenrespective parallel transverse support members 23 a, 24 a.

The separation of the non-linear members 22 a is such that theinsulative member (such as a ceramic) when moulded around the members 22a can also move between the members 22 a and so prevent electricalconduction between the respective non-linear members 22 a at completionof the method 10.

In the depicted embodiment, the shape of the electrically conductivestructure 21 is formed by punching the shape, using a suitable shapedand dimensioned punching tool, from a film of platinum. It is envisagedthat this shape could also be formed by a variety of material removalmethods, such as electrical discharge machining (EDM), micro-knifingand/or laser cutting.

FIG. 14 depicts the non-linear members 22 a as having two relativelyabrupt right angle changes of direction at corners 125 and 126.Alternative elongate but non-linear conductive members 22 a are depictedin FIGS. 15, 16, and 17.

In FIG. 15, the non-linear member 22 a undergoes two changes indirections at corners 125 a and 126 a. In this embodiment, the changesin direction are relatively smoothly curved. As depicted in FIG. 16, thenon-linear member can undergo more than two changes in direction. Othersuitable configurations can be envisaged.

In FIG. 17, the conductive member is formed and then twisted into athird dimension before being clamped and then placed in a mould. Theinsulative member can then be moulded around the spiral conductivemember 22 a. Again, other configurations of the conductive memberextending through the insulative member in a third dimension can beenvisaged.

FIG. 18 depicts an alternative embodiment of the present invention. Inthis embodiment, conductive members 150 are shown extending from oneface 151 of an insulative member 135 to another face 152. In thisembodiment, the conductive members 150 are substantially linear howeverthe surfaces of the conductive members 150 are provided with extendedmaterial to produce a shape that lengthens the interface path betweenthe conductive material and the insulative material 150. As shown,possible shapes of the conductive members according to this embodimentinclude having a stepped outer surface or a screw-thread shaped member.The purpose of providing such a shaped conductive member is tosubstantially increase the leakage pathways of the feedthrough device.

In the depicted embodiment, the step of moulding the ceramic 135 aroundthe electrically conductive structure comprises a step of mounting orclamping the conductive structure in a mould and then moulding theceramic 135 on and/or around the conductive structure.

The mould can again comprise an injection mould. In one embodiment,powder injection moulding (PIM) can be used to mould the ceramic aroundthe desired portion of the conductive structure. In this mouldingprocess, fine ceramic powder is mixed with a binder and homogenised tocreate a feedstock for the injection mould. The presence of the binderserves to make the feedstock sufficiently fluid to be used in aninjection moulding process. Once moulded, the ceramic can be allowed toat least partially set and form a green body.

In the embodiment shown in FIG. 19, the effect of such a design on thefeedstock properties is shown. In this embodiment, which is anenlargement of the section shown in FIG. 18, the feedstock is designedto flow inside the stepped cavities of the conductive member to form abond with the surface of the conductive member along the entire lengthof the conductive member. In this embodiment, the conductive member canhave dimensions of x and y within the range of 10-50 μm. In this range,the feedstock is capable of filling such cavities with standard powderinjection moulding techniques to provide a well sealed interface. It isenvisaged that with improvements in the capabilities of the feedstockand associated equipment, even smaller cavities will be able to besuccessfully employed.

Once the green body is formed, the sacrificial component of theelectrically conductive structure can be removed. In the depictedembodiment, the sacrificial component can be removed by laser cutting.Other suitable techniques, such as cutting or abrading techniques, arealso envisaged.

In the embodiment depicted in FIGS. 14-17, the sacrificial componentcomprises the transverse members 23 a, 24 a. Once these are removed, aplurality of respectively electrically insulated non-linear members 22 aremain extending through the green body.

FIG. 20 depicts a still further type of electrically conductivestructure that can be used in the manufacture of a feedthrough accordingto the present invention. The depicted electrically conductive structureis formed from a film or shim 21 of biocompatible platinum. Othersuitable electrically conductive metals or metal alloys can beenvisaged.

In FIG. 20, the film or shim 21 of platinum is formed into a shapecomprising a sacrificial component and a non-sacrificial component. Inthis embodiment, the electrically conductive structure comprises aplurality of separated members 22 b extending between respectiveparallel transverse support members 23 b, 24 b.

The spacing between the conductive members at their connection totransverse member 23 b is larger than the spacing between the conductivemembers where they connect to transverse member 24 b.

While FIG. 20 depicts the members 22 b as being straight, it will beappreciated that non-linear members could extend between the respectivetransverse members 23 b, 24 b.

The separation of the members 22 b is such that the insulative membermaterial when moulded around the members 22 b can also move between themembers 22 b and so prevent electrical conduction between the respectivemembers 22 b.

In the embodiment depicted in FIG. 20, the shape of the electricallyconductive structure 21 is formed by punching the shape, using asuitable shaped and dimensioned punching tool, from a film of platinum.It is envisaged that this shape could be created by a variety ofmaterial removal methods, such as electrical discharge machining (EDM),micro-knifing and/or laser cutting.

In the embodiment depicted in FIG. 20, the step of moulding theinsulative ceramic member 235 (see FIG. 21) around the electricallyconductive structure comprises a step of mounting or clamping theconductive structure in a mould and then moulding the ceramic on and/oraround the conductive structure. The mould can again comprise aninjection mould. In one embodiment, powder injection moulding (PIM) canbe used to mould the ceramic around the desired portion of theconductive structure. In this moulding process, fine ceramic powder ismixed with a binder and homogenised to create a feedstock for theinjection mould. The presence of the binder serves to make the feedstocksufficiently fluid to be used in an injection moulding process. Oncemoulded, the ceramic can be allowed to at least partially set and form agreen body.

Once the green body is formed, the sacrificial component of theelectrically conductive structure can be removed. In the depictedembodiment, the sacrificial component can be removed by laser cutting.Other suitable cutting or abrading techniques can be envisaged.

In the embodiment depicted in the drawings, the sacrificial componentcomprises the transverse members 23 b, 24 b. Once these are removed, aplurality of respectively electrically insulated members 22 b remainextending through the green body 235 as depicted in FIG. 21.

Such a feedthrough as depicted in FIG. 21 can be adapted to be brazedinto the wall 278 of an implantable stimulator unit of a cochlearimplant hearing prosthesis 270. In this regard, the feedthrough can beadapted to provide electrical conduction between the circuitry withinthe implantable stimulator unit 276 and the intracochlear orextracochlear electrodes 272, and/or the implantable receiver coil 280.

An advantage of the present invention is that it provides thepossibility of allowing exchange of an implantable stimulator unit 276within a recipient with a newer or replacement model without thenecessity to explant the intracochlear electrode array 274. For example,if a recipient already has an implanted stimulator unit 276 with acochlear array 274 connected thereto and electrical connection providedby a feedthrough, it is possible to disconnect the electrode array 274from the external side of the feedthrough and then remove the stimulatorunit 276. While a newer model stimulator unit 276 may have a differentinternal and/or external construction, a feedthrough as here depictedcan be provided in the housing of the stimulator unit that isconnectable on its external side with the existing configuration of theimplanted cochlear array 274 but has a different configuration on itsinternal side that is compatible with the configuration of the internalwiring of the stimulator unit 276.

The conductive members of this feedthrough have a sufficient length andare encased within the insulative member in a way that allows electricalconnection through the feedthrough while preventing transfer of bodilyfluids from outside the component into the interior of the component andvice versa.

FIG. 22 depicts a feedthrough that comprises three separate groups ofconductive structures 22 c disposed in a parallel arrangement. Whileeach group of conductive structures depicted in FIG. 22 is made of aconductive structure, such as is depicted in FIG. 20, it will beappreciated that the feedthrough could be formed of three conductivestructures depicted in FIG. 1 or three conductive structures depicted inFIG. 14. Alternatively, the feedthrough could be formed of one each ofthe conductive structures depicted in FIGS. 1, 14 and 20, respectively.Still further, the feedthrough might be formed of two of one structureof either FIG. 1, 14 or 20 and one of the others depicted in thesefigures.

As depicted in FIG. 23, the respective groups of conductive structures22 c need not be mounted in a parallel configuration. Again, therespective groups of conductive members 22 d can be formed from variouscombinations of conductive structures as depicted in FIG. 1, 14 or 20 orother structures within the scope of the invention.

FIGS. 24 and 25 depict a further embodiment where the length of theconductive members of each group is different to the length of themembers in an adjacent group. The conductive members of a group are alsooffset from its adjacent groups. While the groups are in a parallelrelationship, it will be appreciated that the groups could be in anon-parallel relationship as depicted in FIG. 23. Each of the conductivemembers is also depicted as linear and parallel to other members withinits group. Again, it can be envisaged that instead, the conductivemembers may have different configurations, such as is depicted in FIG.14 or 20. Such configurations make it possible to provide connections in3 dimensions, increasing the density of the connecting elements.

In this embodiment, the platinum members 22 c are embedded in asurrounding sintered insulative member 335.

Once complete, the insulative member 335 with the platinum members 22 cextending therethrough can be brazed into an orifice in the wall of aunit adapted to receive the feedthrough. Electrical connection can thenbe made to each end of the respective platinum members as required toform respective electrical conductive paths through the insulative bodyof the feedthrough.

Such a feedthrough can be adapted to be brazed into the wall 278 of animplantable stimulator unit 276 of a cochlear implant hearing prosthesis270. In this embodiment, the feedthrough can be adapted to provideelectrical conduction between the circuitry within the implantablestimulator unit 276 and the intracochlear or extracochlear electrodes272, and/or the implantable receiver coil 280.

Each feedthrough preferably has sufficient platinum members embeddedtherein to ensure there are sufficient connectors for each of theelectrode channels of the intracochlear electrode array 274, one or moreextracochlear electrodes, and the inputs from the receiver coil.

FIG. 26 depicts yet another embodiment of the present invention, whereinthe feedthrough is formed in a similar manner to that described above,particularly in relation to FIGS. 1-3, however in this embodiment theentire conductive structure is sacrificial, leaving a insulative member200 having a plurality of holes 201 extending therethrough.

In this specific embodiment, the insulative body 200 is formed usingpowder injection moulding and features 28 holes, in predeterminedpositions, extending therethrough.

The insulative body 200 is preferably moulded as described previously.However, in this embodiment, the mould features 28 pins in one plate ofthe mould and a corresponding number of cavities, accommodating thepins, in the opposite plate of the mould. In use, the mould is filledwith hot feedstock and in order to prevent the pressure of the injectionfrom bending the pins and to minimize impact during injection, the mouldis only partially opened when the initial quantity of the feedstock isinjected. As the mould cavity is only partially opened, only a veryshort portion of the pins are exposed to the pressure. The mould is thenslowly opened while injection continues, so that at any given time onlya very short portion of the pins are exposed unsupported to theinjection of the feedstock. Eventually, the entire cavity of the mouldis filled while the position of the pins is preserved. Once the mouldingstep is concluded, the moulded part 200 is ejected, leaving behind themould with its elongate pins in place. The moulded part 200 ejected fromthe mould features the 28 holes 201. Preferably, the holes 201 are only175 μm in diameter. The moulded part 200 then undergoes furtherprocessing.

Platinum pins, are firstly inserted into the holes 201 of the mouldedpart 200 and the entire assembly undergoes a water de-binding step,which includes washing of the moulded part over several hours at 40° C.The assembly then undergoes thermal de-binding at approximately 300° C.over a period of approximately 24 hours. Finally, the assembly issintered at around 1600° C. thereby forming a final assembly that has aseries of platinum pins extending therethrough.

Another embodiment of an insulative member having a plurality of holesextending therethrough can be formed using a modified method from thatset out in FIG. 11. In this embodiment, the method comprises a step ofmoulding or coating an electrically insulating material around astructure, such as a structure having a shape similar to or identical tothat depicted in FIGS. 1, 14, 15, 16, 17 and 20. In this embodiment,however, the entire structure is adapted to be sacrificed so leaving aformed insulative member having a plurality of holes extendingtherethrough corresponding to the position of the sacrificed structure.

In one embodiment, the sacrificial structure can comprise a metal orpolymer having a melting point less than that of the insulative memberformed therearound. Once the insulative member is formed, thetemperature of the member can be increased until such time as the metalor polymer of the sacrificial structure melts and is drained or drawnaway from the insulative member. In this regard, it will be appreciatedthat the insulative member 200 could be formed using an annularsacrificial structure that is melted away so leaving the member 200 withits holes 201 formed in the location of the now melted sacrificialstructure.

The present invention provides a method of forming a feedthrough for animplantable component comprising an insulative member having a pluralityof electrically conductive members extending therethrough. The methodensures the electrically conductive members are encased within theinsulative member in a way that allows electrical connection through thefeedthrough while preventing unwanted transfer of materials between theinterior of the component and the surrounding environment.

It will be appreciated by persons skilled in the art that numerousvariations and/or modifications may be made to the invention as shown inthe specific embodiments without departing from the spirit or scope ofthe invention as broadly described. The present embodiments are,therefore, to be considered in all respects as illustrative and notrestrictive.

1. A method of forming an electrically conducting feedthrough for animplantable medical device comprising: forming an electricallyconductive structure comprising a sacrificial component and anon-sacrificial component comprising at least one electricallyconductive elongate member; coating at least a portion of thenon-sacrificial component with an electrically insulating material suchthat each said at least one electrically conductive elongate member iscontiguous and circumferentially covered by said electrically insulatingmaterial hermetically sealing said at least one electrically conductiveelongate member; removing at least a portion of the sacrificialcomponent from the electrically conductive structure to expose opposingends of said at least one electrically conductive elongate member; andelectrically coupling at least one opposing end of said at least onehermetically sealed and electrically conductive elongate member to theimplantable medical device.
 2. The method of forming an electricallyconducting feedthrough of claim 1, wherein forming an electricallyconductive structure comprises forming the electrically conductivestructure from a film of conductive material.
 3. The method of formingan electrically conducting feedthrough of claim 1 wherein at least oneof the conductive elements is non-linear.
 4. The method of forming anelectrically conducting feedthrough of claim 1 wherein at least one ofthe conductive elements has a length that is greater than the shortestdistance between the respective transverse support members.
 5. Themethod of forming an electrically conducting feedthrough of claim 1wherein at least one of the conductive elements has a surface that isnon-linear.
 6. The method of forming an electrically conductingfeedthrough of claim 1 wherein at least one of the conductive elementshas a surface that defines an interface path between the conductiveelement and the insulating material that is longer than the shortestdistance between the respective transverse support members.
 7. Themethod of forming an electrically conducting feedthrough of claim 1wherein forming an electrically conductive structure comprises: formingan electrically insulating disc having an outer periphery defining aplurality of outwardly extending teeth having notches therebetween; andwinding an electrically conductive element around the disc such that atleast some of the notches have a portion of the conductive elementpassing therethrough.
 8. The method of forming an electricallyconducting feedthrough of claim 7 wherein the electrically insulatingdisc is formed of a ceramic material.
 9. The method of forming anelectrically conducting feedthrough of claim 8 wherein the electricallyconductive element is a platinum metal wire.
 10. The method of formingan electrically conducting feedthrough of claim 9 wherein the elongatemembers extend outwardly and in a direction out of the plane of thefilm.
 11. The method of forming an electrically conducting feedthroughof claim 10 wherein at least three sides of the film have elongatemembers extending at least out of the plane of the film.
 12. The methodof forming an electrically conducting feedthrough of claim 1 whereinforming an electrically conductive structure comprises spirally coilingan electrically conductive metal wire along at least a portion of alength of a screw thread.
 13. The method of forming an electricallyconducting feedthrough of claim 1 wherein coating at least a portion ofthe non-sacrificial component with an electrically insulating materialcomprises mounting or clamping the electrically conductive structure ina mould and then moulding a coating of the insulating material aroundthe conductive structure.
 14. The method of forming an electricallyconducting feedthrough of claim 7 wherein the electrically insulatingmaterial is moulded around the disc such that at least those portions ofthe conductive element passing through the notches of the disc areencapsulated in the insulating material.
 15. The method of forming anelectrically conducting feedthrough of claim 9 wherein the insulatingmaterial is moulded to both sides of the film and elongate members,thereby encapsulating at least a portion of the members in theinsulating material.
 16. The method of forming an electricallyconducting feedthrough of claim 12 wherein once the wire is positionedaround the screw thread, an insulating layer is moulded around thethread and the wire.
 17. The method of forming an electricallyconducting feedthrough of claim 16 wherein once the insulating layer hasat least partially cured, the screw thread is withdrawn from theinsulating material so leaving the coiled wire embedded within the innersurface of the insulating layer, the inner surface defining an orifice.18. The method of forming an electrically conducting feedthrough ofclaim 17 wherein the orifice left by the withdrawal of the screw threadis filled with insulating material.
 19. A method of forming anelectrically conducting feedthrough for an implantable medical devicecomprising: obtaining an electrically conductive structure comprising asacrificial component and a non-sacrificial component comprising atleast one electrically conductive elongate member; coating at least aportion of the non-sacrificial component with a electrically insulatingmaterial such that each said at least one electrically conductiveelongate member is contiguous and circumferentially covered by saidelectrically insulating material hermetically sealing said at least oneelectrically conductive elongate member; and removing at least a portionof the sacrificial component from the electrically conductive structureto expose opposing ends of said at least one electrically conductiveelongate member.
 20. The method of forming an electrically conductingfeedthrough of claim 19, further comprising electrically coupling atleast one opposing end of said at least one hermetically sealed andelectrically conductive elongate member to the implantable medicaldevice.